Method for sizing a multi-ply fiber web and a forming section for a multi-ply fiber web

Abstract

A method for forming a multi-ply fiber web in which least part of the sizing of the multi-ply fiber web is provided by applying sizing agent in the form of foam by a curtain type application device (C10, C20) in between at least two layers of the multi-ply fiber web in the forming section. The invention also relates to a forming section for a multi-ply fiber web having at least one twin-wire forming part formed between a wire (10) for the bottom layer and a wire (20) for the top layer of the multi-ply fiber web, where the layers are joined, and the treated layers combined. The forming section has a curtain type application device (C10, C20) for applying sizing agent in the form of foam in between two layers of the multi-ply fiber web in the forming section of a multi-ply fiber web production line.

Claims

1. A method for forming a multi-ply fiber paper or board web, comprising the steps of: forming a first fiber layer of the paper or board web on a first wire in a fiber web former so the first fiber layer has a first side in contact with the first wire, and a second side opposite the first side; forming a second fiber layer of the paper or board web on a second wire in the fiber web former so the second fiber layer has a first side in contact with the second wire, and a second side opposite the first side; applying a sizing agent, at least part of which forms a foam, by at least one curtain application device to at least one of the second side of the first fiber layer and the second side of the second fiber layer; forming a multi-ply fiber web in a twin-wire forming part of the former by bringing the second side of the first fiber layer on the first wire into engagement with the second side of the second fiber layer on the second wire so that the sizing agent is between the first fiber layer and the second fiber layer and the first wire and the second wire form the twin-wire forming part of the former; and conveying in the twin-wire forming part of the former the sizing agent from one of the first fiber layer of the paper or board web and the second fiber layer of the paper or board web over a boundary therebetween into the other of the first fiber layer of the paper or board web and the second fiber layer of the paper or board web so that the sizing agent enhances ply-bond strength.

2. The method of claim 1 wherein the step of applying the sizing agent by at least one curtain application device is done such that the at least one curtain application device does not contact the first fiber layer and does not contact the second fiber layer.

3. The method of claim 2 wherein the step of applying the sizing agent comprises passing the sizing agent through a slot in the at least one curtain application device.

4. The method of claim 1 wherein at least one device for removing water is positioned below at least one of the first wire and the first side of the first fiber layer and the second wire and the first side of the second fiber layer at a location below the at least one curtain application device.

5. The method of claim 1 wherein conveyance and penetration of the sizing agent into the multi-ply fiber web over a boundary formed between the first fiber layer and the second fiber layer is guided by a suction device at a beginning of the twin-wire forming part.

6. The method of claim 1 further comprising the step of using an air guide to turn a boundary air flow off a running direction of at least one of the first fiber layer second side and the second fiber layer before the step of applying a sizing agent by said at least one curtain application device.

7. The method of claim 1 wherein conveyance and penetration of the sizing agent into the multi-ply fiber web over the boundary formed between the first fiber layer and the second fiber layer is by a combining roll at the beginning of the twin-wire forming part positioned inside the second wire which forms an upper wire loop, the combining roll being positioned after the application of the sizing agent in the form of foam by the curtain application device.

8. The forming section of claim 7 wherein conveyance and penetration of the sizing agent into the multi-ply fiber web over the boundary formed between the first fiber layer and the second fiber layer is guided by a sleeve roll positioned inside the first wire which forms a lower wire loop.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In FIG. 1 is shown schematically an advantageous example of a forming section according to the invention.

(2) In FIG. 2 is shown schematically another advantageous example of a forming section according to the invention.

(3) In FIG. 3 is shown schematically a curtain application device and an air guide-steam box arrangement according to an advantageous example.

(4) In FIG. 4 is shown schematically yet another advantageous example of a forming section according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

(5) During the course of the following description like numbers and signs will be used to identify like elements according to the different views which illustrate the invention and its advantageous examples. In the figures some repetitive reference signs have been omitted for clarity reasons.

(6) In FIG. 1 is shown an example of a forming section for a multi-ply fiber web, in this example for a two-layer fiber web. The forming section comprises two headboxs M10, M20 one for each layer, from which a stock suspension is fed to the forming unit for each layer beginning as one wire part comprising a wire 10 for the bottom layer of the multi-ply fiber web and a wire 20 for the top layer of the multi-ply fiber web. Each wire has rolls 12, 22 for guiding, tensioning and/or driving the wire 10, 20 as an endless loop. The stock suspension from the headboxs M10, M20 are first fed onto the wires 10, 20 and thereafter the stock on the wires is guided past water removal means 11, 21, 15, and 25 located inside loops formed by the wires. Inside of the loops of wires 10, 20 at least one suction means 15, 25 is located. During the run of the stock on the wires part the water removal is substantially horizontal. Curtain application devices C10, C20 are located along the run of the stock layers on the wires for applying sizing agent, in the form of foam, by a curtain type application device onto the stock layer thus between the layers of the multi-ply fiber web in the forming section. The curtain application device C10, C20 is advantageously located such that the suction means 15, 25 are located on the opposite side of the multi-ply fiber web inside of the loop of the wires 10, 20. In that way the sizing agent contacts the stock layer on the suction means 15, 25 area.

(7) Advantageously, only one application device C10, C20 for the foam is used, which device C10 most advantageously applies the foam onto the fiber web layer on the lower wire 10. The application device C20 for the foam can also be only applicating onto the fiber web on the upper wire 20. It is also possible to use two application devices C10, C20 as shown in the example of FIG. 1. Also, more than one application device C10, C20 can be used consecutively for one of the fiber web layers.

(8) The stock forming the top layer of the multi-ply fiber web on the wire 20 is after the top layer is formed guided downwards towards the first wire 10 and the runs of the wire 10 for the bottom layer and the wire 20 for the top layer are united by a combining roll 23 to form a twin-wire part of the forming section and the webs for the bottom layer and the top layer are guided into a gap formed between the wires 10, 20 forming the twin-wire part of the forming unit. Thus the web layers are joined together by a combining roll 23 at the beginning of the twin-wire forming part. The combining roll 23 is situated within the top layer wire loop 20. Thus, the sizing agent applied in the form of foam by the curtain application devices C10, C20 onto each layer of the web is guided in between the layers. Advantageously, after applying the sizing agent in the form of foam by the curtain application device C10 the sizing agent's conveyance and penetration into the web layer is assisted such that the sizing agent extends deeper into the web layer on which the sizing agent is applied in the form of foam by guiding the foam in the desired direction. In the example of FIG. 1 a suction device(s) 17 are provided inside the lower wire loop 10 and after the application of the sizing agent in the form of foam by the curtain application device C10 but before the web layers are joined by the combining roll 23 at the beginning of the twin-wire forming part in order to assist the conveyance and penetration of the sizing agent into the web layer.

(9) Additionally advantageously, after applying the sizing agent in the form of foam by the curtain application device C20 and after the web layers have been joined by the combining roll 23 conveyance of the sizing agent is further enhanced by guiding the direction of conveyance of the sizing agent over the joining boundary towards the web layer on the wire 10 on the other side of the boundary of the joining web layers. In the example of FIG. 1 suction means 18 are provided inside the lower wire loop 10 and after the application of the sizing agent in the form of foam by the curtain application device C20 and after the web layers have been joined by the combining roll 23 at the beginning of the twin-wire forming part in order to enhance the conveyance of the sizing agent over the boundary between the joined web layers.

(10) Additionally advantageously, after applying the sizing agent in the form of foam by the curtain application device C20, it would be possible to replace the traditional combining roll 23 by a sleeve roll (not shown). In that embodiment the sleeve roll is provided inside the upper wire loop 20 after the application of the sizing agent in the form of foam by the curtain application device C20 and after the web layers have been joined by the sleeve roll at the beginning of the twin-wire forming part in order to enhance the conveyance of the sizing agent over the boundary between the web layers joined and deeper towards the bottom surface of the multi-ply fiber web. A sleeve roll is a roll that comprises a stationary support shaft, a belt loop, which is led to circle around the stationary support shaft, wherein the sleeve roll further comprises at least one curvilinear dewatering zone consisting of two partial curves such that the radius of curvature of a first partial curve is greater than the radius of curvature of a second partial curve following the first partial curve in the travel direction of the belt loop. A sleeve roll configuration is disclosed for example in EP patent application 2017164069 published as EP3382094. After the joining of the layers the multi-ply fiber web is guided on the wire 10 supporting the bottom side of the multi-ply fiber web. Support foils 16 located inside the wire 10 loop engage the wire beneath the multi-ply fiber web. The support foils 16 do not deviate the run of the wire 10 but only remove water from the bottom surface of the wire 10 and support the run of the wire 10 as the multi-ply fiber web is guided via the suction roll 13 towards a pick-up roll 41 for transferring the multi-ply fiber web to a first press fabric 40 of a press section. The press section also comprises a second press fabric 50 with a roll 51. The press fabrics 40, 50 comprise rolls 42, 52 for guiding, tensioning and/or driving the fabrics 40, 50 in an endless loop. In the press section the multi-ply fiber web is guided between the first press fabric 40 and the second press fabric 50 to a press nip formed between a first press roll 45 and a second press roll 55. After the press section the fiber web is guided to a drying section (not shown).

(11) In FIG. 2 is shown an example of a forming section for a multi-ply fiber web, in this example a three-layer fiber web is formed. The forming section comprises headboxes M10, M20, M30 one for each layer, from the headboxes the stock suspension is fed to the forming unit for each layer beginning with one wire part comprising a wire 10 for the bottom layer of the multi-ply fiber web and a wire 20 for the middle layer of the multi-ply fiber web and a wire 30 the top layer of the multi-ply fiber web, each wire comprising rolls 12, 22, 32 for guiding and driving the wire 10, 20, 30 as an endless loop. The stock suspension is first fed onto the wires 10, 20, 30 and thereafter water is removed via removal means 11, 15, 21, 25, 31, 35, which can be for example forming shoes and/or suction devices, each loop comprising at least one suction device 15, 25, 35. The run of the wire 10, 20, 30 during this water removal on each of the wires a part of the wires is substantially horizontal. A curtain application device C10, C20, C30, C40 is located over the stock layers where the wires are substantially horizontal for applying sizing agent in the form of foam by a curtain type application device onto the stock layer such that sizing agent is applied to each stock layer before said layers are joined so that the sizing agent is between at the layers of the multi-ply fiber web in the forming section. The curtain application device C10, C20, C30, C40 is advantageously located such that the suction means 15, 25, 35 are located on the opposite side of the multi-ply fiber web inside of the loop of the wires 10, 20, 30. In that way the sizing agent contacts stock layer on the suction means 15, 25, 35 areas.

(12) Advantageously, only one application device C10, C20, C30, C40 for the foam is used, which device C10 most advantageously applies the foam onto the fiber web layer on the lower wire 10. The application device C20 for the foam can also be only applicating onto the fiber web on the wire 20 or the application device C30 for the foam can also be only applicating onto the fiber web on the wire 30. Additionally, yet another application device C40 can be used to apply the sizing agent in the form of foam on to the web layer on the lower wire after joining the web layer on the lower wire 10 and the web layer on the upper wire 20. It is also possible to use two application devices C10, C20, C30, C40 or three application devices C10, C20, C30, C40 or all four application devices C10, C20, C30, C40 as shown in the example of FIG. 2. Also, more than one application device C10, C20, C30, C40 can be used consecutively for one fiber web layer.

(13) The stock forming the middle layer of the multi-ply fiber web guided on the wire 20 is after the one-wire substantially horizontal part, guided downwards towards the first wire 10 and the runs of the wire 10 for the bottom layer and the wire 20 for the middle layer are united by a combining roll 23 to form a twin wire part. The webs for the bottom layer and the middle layer are guided into a gap formed between the wires 10, 20 forming the twin-wire part of the forming unit. Web layers have been joined together by a combining roll 23 at the beginning of the twin-wire forming part. The combining roll 23 is situated inside the middle layer wire loop 20. Thus, the sizing agent applied in the form of foam by the curtain application devices C10, C20 onto the bottom and middle layer of the web is guided in between the layers.

(14) Advantageously, after applying the sizing agent in the form of foam by the curtain application device C10 its conveyance and penetration into the web layer is assisted such that the sizing agent is moved deeper into the web layer on which the sizing agent is applied in the form of foam by guiding the foam deeper into the web layer. In the example of FIG. 2 a suction means 17 is provided inside the lower wire loop 10 and after the application of the sizing agent in the form of foam by the curtain application device C10 but before the web layers are joined by the combining roll 23 at the beginning of the twin-wire forming part in order to assist the conveyance and penetration of the sizing agent into the web layer.

(15) Additionally advantageously, after applying the sizing agent in the form of foam by the curtain application device C20 and after the web layers have been joined by the combining roll 23 conveyance of the sizing agent is further enhanced by guiding the direction of conveyance of the sizing agent from the surface over the joining boundary towards the web layer on the other side of the boundary of the joining web layers. In the example of FIG. 2 a suction means 18 is provided inside the lower wire loop 10 and after the application of the sizing agent in the form of foam by the curtain application device C20 and after the web layers have been joined by the combining roll 23 at the beginning of the twin-wire forming part in order to enhance the conveyance of the sizing agent over the boundary between the web layers joined.

(16) After the joining of the layers the multi-ply fiber web is guided on the wire 10 supporting the bottom side of the multi-ply fiber web on a substantially horizontal wire part, during which run support foils 14 are located inside the wire 10 loop. The support foils 14 do not deviate the run of the wire 10 but only remove water from the bottom surface of the wire 10 and support the run of the wire 10 as the multi-ply fiber web is guided towards the next twin wire part. The stock forming the top layer of the multi-ply fiber web guided on the wire 30 is after a substantially horizontal wire part guided downwards towards the first wire 10 and the runs of the wire 10 which now carries the bottom and middle layers and the wire 30 for the top layer are united by a combining roll 33 to form a second twin wire part and the webs for the bottom and middle layers and the top layer are guided into a gap formed between the wires 10, 30 forming the second twin-wire part of the forming unit. Thus the web layers have been joined together by a combining roll 33 at the beginning of the second twin-wire forming part. The combining roll 33 is situated inside the top layer wire loop 30. Thus, the sizing agent applied in the form of foam by the curtain application device C30 onto the top layer of the web is guided in between the top layer and the combined bottom-middle layer and the sizing agent applied in the form of foam by the curtain application device C40 is guided in between the top layer and the combined bottom-middle layer.

(17) Advantageously, after applying the sizing agent in the form of foam by the curtain application devices C30, C40 and after the web layers have been joined by the combining roll 33 conveyance of the sizing agent is further enhanced by guiding the direction of conveyance of the sizing agent from the surface in to the web layer on the lower wire 10 and over the joining boundary towards the web layer on the other side of the boundary of the joining web layers. In the example of FIG. 2 a suction means 18 is provided inside the lower wire loop 10 and after the application of the sizing agent in the form of foam by the curtain application devices C30, C40 and after the web layers have been joined by the combining roll 33 at the beginning of the twin-wire forming part in order to enhance the conveyance of the sizing agent over the boundary between the web layers joined.

(18) After the joining of the layers the multi-ply fiber web is guided on the wire 10 supporting the bottom side of the multi-ply fiber web on a substantially horizontal wire part, along the horizontal wire part run, support foils 16 are located inside the wire 10 loop. The support foils 16 do not deviate the run of the wire 10 only remove water from the bottom surface of the wire 10 and support the run of the wire 10 as the multi-ply fiber web is guided via the suction roll 13 towards a pick-up roll 41 for transferring the multi-ply fiber web to a first press fabric 40 of a press section. The press section also comprises a second press fabric 50 with a roll 51. The press fabrics 40, 50 comprise rolls 42, 52 for guiding, tensioning and/or driving the fabrics 40, 50 in an endless loop. In the press section the multi-ply fiber web is guided between the first press fabric 40 and the second press fabric 50 to a press nip formed between a first press roll 45 and a second press roll 55. After the press section the fiber web is guided to a drying section (not shown).

(19) Correspondingly the application of the sizing agent in the form of foam can be provided for multi-ply fiber webs with more layers than in the examples of FIGS. 1 and 2.

(20) In FIG. 3 is shown a curtain application device C10, C20, C30, C40 and an air guide 61, and a steam box 62 arrangement 60. The curtain application device C10, C20, C30, C40 is advantageously located such that the suction means 15, 25, 35 are located on the opposite side of the multi-ply fiber web W and the wire 10, 20, 30. In the example as the air guide a reversing blade or air foil 61 is used before the curtain application device C10, C20, C30, C40 for turning boundary air flow A off the running direction of the multi-ply fiber web W before curtain application of the sizing agent. An air curtain can also be used as the air guide. A steam-box 62 is provided just after the air guide 61.

(21) In FIG. 4 is shown an example of a forming section for a multi-ply fiber web, in this example for a two-layer fiber web. The forming section comprises a headbox M10, M20 for each layer, from which the stock suspension is fed to the forming unit for each layer beginning as one wire part comprising a wire 10 for the bottom layer of the multi-ply fiber web and a wire 20 for the top layer of the multi-ply fiber web, each wire comprising rolls 12, 22 for guiding, tensioning and/or driving the wire 10, 20 as an endless loop. The stock suspension M10, M20 is first fed onto the wire 10, 20 and thereafter the stock on the wire is guided past water removal means 11, 21, 15, 25 inside the loop of the wire 10, 20. Inside of the loop of the wire 10, 20 at least one suction means 15, 25 is located. During the run of the stock on a portion of the wire which is substantially horizontal, water is removed. A curtain application device C10, C20 is located over the stock layer, on the portion of the wire which is substantially horizontal for applying sizing agent in the form of foam by a curtain type application device onto the stock layer on the wire so that the sizing agent ends up between the layers of the multi-ply fiber web. The curtain application device C10, C20 is advantageously located such that the suction means 15, 25 are located on the opposite side of the multi-ply fiber web inside of the loop of the wires 10, 20. In that way the sizing agent contacts stock layer on the suction means 15, 25 area.

(22) Advantageously, only one application device C10, C20 for the foam is used, which device C10 is most advantageously applicating the foam onto the fiber web layer on the lower wire 10. The application device C20 for the foam can also be a curtain coater which applies sizing agent onto the fiber web on the upper wire 20. It is also possible to use two application devices C10, C20 as shown in the example of FIG. 4. Also, more than one application device C10, C20 can be used consecutively for one of the fiber web layers.

(23) The stock forming the top layer of the multi-ply fiber web guided on the wire 20 is after the substantially horizontal wire part guided downwards towards the first wire 10 and the runs of the wire 10 for the bottom layer and the wire 20 for the top layer are united by a combining roll 23 to form a twin wire part and the webs for the bottom layer and the top layer are guided into a gap formed between the wires 10, 20 forming the twin-wire part of the forming unit. Web layers have been joined together by a combining roll 23 at the beginning of the twin-wire forming part. The combining roll 23 is situated in the top layer wire loop 20. Thus, the sizing agent applied in the form of foam by the curtain application devices C10, C20 onto each layer of the web, is guided in between the layers.

(24) Advantageously, after applying the sizing agent in the form of foam by the curtain application device C10 its conveyance and penetration into the web layer is assisted such that the sizing agent is moved deeper into the web layer on which the sizing agent is applied in the form of foam by guiding the foam to move into the web layer. In the example of FIG. 4 a suction means 17 is provided after the application of the sizing agent in the form of foam by the curtain application device C10 but before the web layers are joined by the combining roll 23 at the beginning of the twin-wire forming part in order to assist the conveyance and penetration of the sizing agent into the web layer.

(25) Additionally advantageously, after applying the sizing agent in the form of foam by the curtain application device C10 and after the web layers have been joined by the combining roll 23 conveyance of the sizing agent is further enhanced by guiding the direction of conveyance of the sizing agent from the surface over the joining boundary towards the web layer on the other side of the boundary of the joining web layers. In the example of FIG. 4 a sleeve roll 27 is provided inside the lower wire loop 10 after the application of the sizing agent in the form of foam by the curtain application device C10 and after the web layers have been joined by the combining roll 23 at the beginning of the twin-wire forming part in order to enhance the conveyance of the sizing agent over the boundary between the web layers joined and deeper towards the top surface of the multi-ply fiber web. Alternatively, this can be provided by locating a suction means (not shown) inside the upper wire loop and thus causing the conveyance of the sizing agent towards the top surface of the multi-ply fiber web. A sleeve roll 27 is a roll that comprises a stationary support shaft, a belt loop, which is led to circle around the stationary support shaft, that the sleeve roll further comprises at least one curvilinear dewatering zone consisting of two partial curves such that the radius of curvature of a first partial curve is greater than the radius of curvature of a second partial curve following the first partial curve in the travel direction of the belt loop. A sleeve roll configuration is disclosed for example in EP patent application 2017164069 published as EP3382094.

(26) After the joining of the layers the multi-ply fiber web is guided on the wire 10 supporting the bottom side of the multi-ply fiber web substantially horizontal wire part during which run support foils 16 are located inside the wire 10 loop. The support foils 16 do not deviate the run of the wire 10 only remove water from the bottom surface of the wire 10 and support the run of the wire 10 as the multi-ply fiber web is guided via suction roll 13 towards a pick-up roll 41 for transferring the multi-ply fiber web to a first press fabric 40 of a press section. The press section also comprises a second press fabric 50 with a roll 51. The press fabrics 40, 50 comprise rolls 42, 52 for guiding, tensioning and/or driving the fabrics 40, 50 in an endless loop. In the press section the multi-ply fiber web is guided between the first press fabric 40 and the second press fabric 50 to a press nip formed between a first press roll 45 and a second press roll 55. After the press section the fiber web is guided to a drying section (not shown).

(27) Above only some advantageous examples of the inventions have been described to which examples the invention is not to be narrowly limited and many modifications and alterations are possible within the invention.

(28) It should be understood that, water is removed via removal means, refers to a device or devices used in a paper machine for removing water from a fiber web these devices include mechanical dewatering devices such as forming shoes or foil strips where the movement of the wire over the shoe results in removal of water which may in part be or principally be by production of a vacuum through created hydrodynamic forces. Water is removed via removal means also includes a suction device where is used a machine to create a vacuum and connect the vacuum source to connect to a box, a roll with openings, shoe, sleeve roll, or other structure which then uses the difference in air pressure created by the vacuum source, not usually local to the device, to draw water from the web. Such use of vacuum is often referred to as a suction device such as suction boxes, turning rolls, suction rolls, and rolls provided with an open surface, which are used in many different arrangements and arrays when trying to optimize the volume, time and location of water being removed when forming the web. Vacuum in a suction roll or pick-up roll can also be used to transfer or direct a fiber web in a wire or fabric.